When the delta variant swept through the Southern U.S. in summer 2021, the hot spots were easy enough to see. Huge swaths of red in Florida, Louisiana and Alabama swelled on COVID-19 tracker maps, like stop lights warning travelers to avoid the region.

The culprit also seemed straightforward: Low vaccination rates in conservative communities. The Biden administration fueled this perception by calling COVID-19 a “pandemic of the unvaccinated,” framing the crisis — incorrectly, according to some experts — as a localized problem that could be solved if enough Republicans simply got their shots.

That era was easy to conceptualize compared to our current quagmire. Now, thanks to the omicron variant, hot spots are everywhere. The first states to see rising cases were also those with high vaccination rates, including Vermont, Massachusetts and New York. It’s hard to call this a pandemic of the unvaccinated when one in every 30 New York City residents was diagnosed with COVID-19 in the space of a single week during the peak of the city’s omicron surge, and over 80 percent of adults in the city are fully vaccinated.

The new, omicron-drenched landscape means we can no longer find hot spots just by looking at a map. In fact, the most important hot spots are less visible: They’re among the people most vulnerable to severe disease and in the settings that are capable of shutting down society when outbreaks swell. When COVID-19 is everywhere, visualizing data can only tell you so much.

For example, a COVID-19 map that visualizes entire counties or states obscures the vulnerable populations within. Vaccination rates for these larger areas can be misleading, said Enrique Neblett, a professor of health behavior at the University of Michigan. Highly vaccinated states still have large pockets of unvaccinated people, who are much less protected from severe COVID-19 symptoms.

Instead of thinking about which states are being affected most, think about who is most vulnerable. In other words, start with the elderly. When it comes to risk of severe COVID-19, nursing homes and other long-term care facilities are among the most dangerous settings. Nursing-home residents were among the first in line for vaccines last winter, but immunity has now waned for vulnerable seniors. Booster shot intake has been slow and uneven, too: As of mid-December, the share of nursing home residents fully vaccinated and boosted ranged from 70 percent in Vermont to just 17 percent in Arizona, according to AARP.

While early studies suggest the omicron variant may be less deadly, much of that research is based on hospitalizations among younger people; how the variant behaves among seniors is less clear. So far during the Omicron wave, hospital admission rates among adults over age 60 have been far higher than among younger age groups, according to data from the Centers for Disease Control and Prevention.

Prisons and jails are in a similar position to nursing homes. Infections increased more than tenfold in facilities in New York and Chicago in December, according to the Marshall Project. These facilities have also been slow to offer vaccines and boosters, leaving elderly inmates and those with underlying health conditions particularly vulnerable.

And then there are people walking around who haven’t gotten the vaccine — and not always because they don’t want it. “Most cases continue to be concentrated among people who are low-income workers,” said Julia Raifman, a professor of health law, policy and management at the Boston University School of Public Health. “And actually, unfortunately, they’re least likely to be vaccinated.”

Uninsured Americans under age 65 are the least vaccinated demographic group in the country, according to a November 2021 survey from the Kaiser Family Foundation. That survey found that just 56 percent of uninsured Americans under 65 had received at least one dose of the vaccine; among Republicans, the rate was 59 percent. Vaccination rates are also low for rural Americans and those without college degrees.

Lower-income Americans are often essential workers, putting them at particular risk of catching the coronavirus. Testing barriers don’t help either, said Katelyn Jetelina, a professor of epidemiology at the University of Texas Health Science Center at Houston and author of the newsletter Your Local Epidemiologist. “Those with really public facing jobs,” she said, are also “those that can’t stand in line for hours to go get a test in New York City.”

“Because [these workers] can’t get access to testing, they don’t know if they’re a case,” she said. “They end up at the hospital later than they should. And then they die at higher rates.”

Service workers who contract COVID-19 in high numbers have an outsized impact on their communities, even if their cases don’t lead to severe symptoms. Such impacts can range from Christmas flight cancelations, to subway closures, to declines in restaurant service. Omicron is also hitting hospitals across the country so profoundly that some facilities are asking COVID-19-positive employees to come back to work — emboldened by recent CDC guidance.

Cases among children also have immense ripple effects. Since November, all children ages five and up have been eligible for vaccination. But less than one-third of children ages five to 11 have received at least one vaccine dose so far, as of Jan. 12. While the risk of severe COVID-19 symptoms is much lower for children than for other age groups, a single student getting sick can lead to learning loss, missed work for caretakers and further consequences for hundreds of other children, family members, and school staff.

According to Burbio’s school opening tracker, about 5,400 schools either switched from in-person to remote instruction or closed entirely during the week of Jan. 3 due to the pandemic. That’s 90 percent higher than the previous record number of school disruptions, set in November 2021.

One way we might be able to see hidden hot spots is by looking at data on COVID-19 cases by occupation — which the U.S. government does not collect. The federal government has never reported comprehensive statistics on COVID-19 cases in schools, for example. That leaves surveys and independent research projects to fill the information gaps. 

Still, the toolkit for addressing omicron hot spots is the same as it has been throughout the pandemic, Raifman said. New federal requirements for vaccinations, masks, testing and ventilation would help protect the people most vulnerable to severe symptoms while also reducing case numbers in settings that can shut down society.

“Federal guidance on mask mandates tomorrow would likely reduce deaths by tens of thousands,” Raifman said. “The perfect doesn’t need to be the enemy of the good, you don’t need every state to pass it. But you can put in place a mask policy during the surge, and it will reduce transmission and reduce the harms to health care workers and businesses.”

In other words: When you can’t pinpoint specific hot spots, you need broad measures that can impact everyone. That strategy was made harder on Thursday, as an Occupational Safety and Health Administration rule that would have required around 80 million workers to get vaccinated or comply with regular testing was blocked by the Supreme Court. Without this rule, low-income workers will continue to face heightened risk of COVID-19 infection — and their cases will continue to ripple out.